Car comparison calculator
Two cars, one comparison. Finance, insurance, fuel or charging, tax and servicing, totalled and set side by side so you can see which is actually cheaper to keep.
How this is calculated
Each car is totalled independently across five lines: finance multiplied by twelve, insurance, fuel or charging, vehicle tax and servicing. The two totals are then set against each other.
Fuel cost for petrol and diesel converts your annual mileage into gallons using the mpg figure, then into litres at 4.546 litres per gallon, then multiplies by the pump price you entered.
Charging cost divides annual mileage by miles per kWh and multiplies by the electricity rate you entered. Home and public rates differ enormously, so use the one you will actually pay.
Depreciation is not included. It is usually the largest single cost of car ownership, but it depends on resale value rather than anything you can enter reliably up front.
Rates used · 2026/27
| Imperial gallon | 4.546 litres |
| Typical petrol economy | 40 to 55 mpg |
| Typical EV efficiency | 3.0 to 4.5 miles per kWh |
| Depreciation | not included |
Last checked July 2026. Source: HMRC and gov.uk.
Worked example
At 8,000 miles a year, a 45 mpg petrol car at 139.9p a litre burns £1,131 of fuel. An electric car at 3.6 miles per kWh on a 24.5p home rate uses £544, a £586 saving. But with £110 a month more finance and £160 more insurance, the electric car totals £5,249 a year against the petrol car's £4,526. The fuel saving is real and still £724 short of covering the rest.
Common questions
Why is depreciation not included?
Because it depends on what the car is worth when you sell it, which nobody can enter accurately in advance. Including a guess would make the comparison look precise while being the least reliable number on the page.
What efficiency figure should I use?
Real-world, not the official figure. Manufacturer economy figures are optimistic for both petrol and electric, and cold weather reduces EV range noticeably.
Can I compare two petrol cars?
Yes. Set both to petrol or diesel and enter each car's mpg. The fuel type selector only changes how efficiency is interpreted.
Does it handle public charging?
Enter your public rate in the electricity field. Rapid charging often runs three to four times the home rate, which changes the answer completely for anyone without a driveway.